This research aims to investigate the perceptual effects of compression in human auditory system. Fundamental to this aim is the development of a behavioral (psychoacoustic) measure of compression. Two alternative measures will be tested for this purpose, one using a variant of the pulsation threshold measure and the other using a nonsimultaneous masking task. First, the two measures will be tested with normal-hearing listeners using signal frequencies ranging from 500 Hz to 8 kHz over a wide range of signal levels. Next, the results from normal-hearing listeners will be compared with those from listeners with sensorineural hearing loss. Both sets of data will be validated by comparing them with relevant physiological data and with previous behavioral measures of auditory compression. It is hoped that a measure of residual compression in hearing-impaired listeners will allow the separation of transduction and active components of a given sensorineural hearing loss. The resulting estimates of compression from hearing-impaired listeners with hearing losses between 40 and 60 dB HL will be used to provide parameters for a recent model of loudness recruitment. The predictions of the model will then be compared on an individual basis with loudness matching data from the same hearing- impaired listeners. The individual estimates of auditory compression from the hearing-impaired listeners will also be used to provide predictions for other psychoacoustic tasks thought to be influenced by compression, namely the additivity of nonsimultaneous masking and the temporal decay of forward masking. These predictions will then be compared with data from the same listeners. The results should provide a deeper understanding of the changes in auditory perception caused by hearing loss. A reliable behavioral measure of auditory compression may also provide a useful clinical tool in the diagnosis of hearing impairment, and may assist in selecting the appropriate processing algorithms for digital hearing aids on an individual basis.